Circling Approach

[GMS]

Ladies and Gents,

I am looking for some help with regards to Circling Approaches. I fly for a UK based airline so I am therefore dealing with ICAO rules, but would nevertheless be interested to hear any comments from USA based pilots as well.

I have two questions for which I cannot find specific answers.

 Once at MDA/MDH, is there any rule that does not allow you to descend below this Alt/Height in case you have some cloud present that you wish to avoid? I am talking of only 100 ft. or so during the downwind leg, prior to the descent for landing.

 Are there any rules as to when to commence descent from MDA/MDH? I have seen one article that mentions that you can't commence descent until within 45º of the runway centreline.

I have read the ICAO Pans-Ops Document 8168 but unfortunately it does not shed any light on these issues.

I would be very grateful to have your views on this matter and for any help.

Many Thanks

GMS

[Straight & Level]

GMS
There are a number of documents from which to extract the required information. CAP 360 states that the Visual Manoeuvering minima is calculated by finding the dominant obstacle in the manoeuvering area. This manoeuvering area is determined by drawing arcs centered on each runway threshold. For a Cat C aeroplane for example this arc is set at a radius of 4.2nm. When the dominant obstructions have been identified, MDA is calculated for each different category of aircraft, so for a Cat C aircraft the minima would be 400ft above the obstacle with a minimum MDH above aerodrome elevation of 600ft. PANS OPS specifies a minimum visibility of 3700m (Cat C) but I guess you will be operating to JAR OPS minima which specifies a minimum met vis of 2400m and 600 ft MDH. The law states that if visual contact cannot be maintained then one would initiate a go-around to comply with the instrument approach procedure to the initial approach runway. This can be quite complicated if you're on final approach to the landing runway at some airfields and this should be considered during the brief. As far as the descent from circling minima is concerened, one can descend from a point which would allow a continuous 3 degree descent profile to the landing runway. This is taken into account in the calculation of the circling minima. This was written down in an AIC I think sometime ago but I can't remember the reference.
This is the way that I understand it but would welcome any corrections or omissions.
I hope this helps.

[Tinstaafl]

Australian rules (from memory, so pleas excuse any errors). According to Oz AIP these are ICAO compliant.

May Descent below MDA:

1. Within the circling area for category: Cat A = 1.68nm, Cat B = 2.66nm, Cat C = ??, Cat D = 4.xx (?), Cat E = 5.xx (also ?)

2. Clear of cloud, in sight of the approach end of the runway, or lights or markings associated with the approach end of the RWY.

3. In sight of the ground or water

4. Visibility not less than that specified for circling.

5. IAS as specified for cirling for a/c category.

5. By day: Descent to not less than Obstacle Clearance Height (OCH)
For Cat A & B = 300' above highest obstacle in the circling area, Cat C&D = 400', Cat E = 500'

By Night: Maintain MDH until intercepting the normal descent profile for a landing approach to that runway. In this case descent would commence where ever the gradient meets the aircraft's flight path eg final, crosswind, downwind etc.

Someone please correct my lapses in memory!

Hope this helps.

T

[GMS]

Many thanks to both of you.

GMS

[tired]

GMS, as far as I'm aware, though I can't quote the reference for it, under JARs you MUST remain at the circling MDA until you can commence a continuous descent to land. (I think this is what S&L was saying, too!)

Our (JAR) Ops manual has a specific note saying that once you're visual you may not convert it into a visual approach, using visual minima - it effectively remains an instrument procedure until touchdown. As S&L mentioned, if you do lose sight of the runway you must carry out an immediate missed approach, using the MAP of the instrument approach you used - which can be quite tricky at times, believe me!!

Hope this helps.

[Roadtrip]

The US Airman's Information Manual states in 5-4-18f:

"Pilots should remain at or above the circling altitude until the aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers."

It's also interesting to note that most type-ratings for Part 121 carriers restrict circling approaches in VMC only.

[Zeitgebers]

Here is how I understand it.
To quote JAR-OPS 1 Subpart E 1.430 (b)(3):
Visual Reference. A pilot may not continue an approach below MDA/MDH unless at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot :
(i) Elements of the approach light system
(ii) The threshold
(iii) The threshold markings
(iv) The threshold lights
(v) The threshold identification lights
(vi) The visual glide slope indicator
(vii) The touchdown zone or touchdown zone markings
(viii)The touchdown zone lights
(ix) Runway edge lights
(x) Other visual references accepted by the authority

So providing you can see the LANDING threshold then you are permitted to go below MDA if needs be to avoid a bit of cloud and remain in visual contact. ( you would be responsible for your own obstacle clearance )
The descent point will depend on the height above touchdown but as stated by S&L is calculated based on a 3 degree descent. We start descent as we turn base.

[4Greens]

In this day and age, circling approaches in passenger carrying aircraft, particularly big ones, should be of f the agenda. The amount of confusion about how to do one is indicative of systemic safety problems. Spend your time persuading your airline/regulator/safety group stopping the practice. GPS arrivals obviate the need.

[GMS]

Thank you all for your comments. GMS

[tired]

Zeitgebers - doesn't that section refer to straight-in approaches only? Circling has got it's own section elsewhere in the book.